1. Field of the Invention
This invention relates to detecting loose and otherwise faulty pressure joints in power distribution systems, and particularly, by monitoring the impedance across the pressure joints using the power delivered to a load.
2. Background Information
Power systems distributing electrical power throughout an installation, such as for instance a building, typically include different types of conductors and devices, such as switches, circuit breakers, contractors, overload relays, network protectors, and the like that are mechanically interconnected. The conductors can be rigid bus bars and bus ways made up of sections bolted together, including branch connections. Other conductors include cables bolted or clamped to the bus bars or bus ways and to the various devices mentioned above.
One mode of failure in these systems occurs when the pressure junctions increase in resistance. Loose fittings, dirt, corrosion or moisture are all common causes of this increase in resistance. The resultant heat generated by such failures reduces the efficiency of the power distribution system and can lead to interruption of power. The state of the art method of detecting this problem is infrared scanning. However, this technique usually requires partial disassembly of the equipment to gain access to hidden connections and is not suitable for continuous monitoring. It has been suggested in U.S. Pat. No. 5,600,255 that loose connections in live ac power systems can be detected by injecting a known dc current into the ac power bus and measuring the dc voltage drop across the pressure junction. This technique requires a constant dc current source and filters to isolate the dc voltage reading from the ac voltage on the live bus.
An improved method and apparatus is needed for determining the resistance across joints in a power distribution system.